DE69803438T2 - RADIATION DETECTOR AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

Technical field

The present invention relates to a radiation detection device, and more particularly to a radiation detection device having a light receiving portion with a large area, such as is used for medical X-ray examinations and the like.

State of the art

While conventional X-ray sensitive films are used for medical and industrial X-ray examinations, systems using a radiation detection device for radiation imaging are gaining popularity due to their convenience and the storage capacity of their photographic results. Such a radiation imaging system uses an area consisting of many pixels to obtain two-dimensional imaging data from a radiation as an electrical signal, processes the obtained signal with a processing unit to display it on a screen. A typical radiation detection device is configured such that a scintillator is arranged on a one- or two-dimensional array of photodetectors to convert the incident radiation into light, which is then detected.

CsI, a typical scintillator material, is a hygroscopic material that dissolves by absorbing vapor (moisture) in the air. As a result, the characteristics of the scintillator, especially the resolution, deteriorate adversely.

Known as a radiation detection device with a structure for protecting the scintillator against moisture, the technique is disclosed in Japanese Laid-Open Patent Application No. 5-196742, corresponding to EP-A-0528676. In this technique, a waterproof barrier with moisture protection is formed on top of the scintillator layer, thereby protecting the scintillator layer against moisture.

In the above technique, it is still difficult for the moisture-proof barrier to come into close contact with the substrate of the radiation detection device in the outer peripheral region of the scintillator layer. In particular, in the radiation detection device with a large area, such as for chest X-ray examinations or the like, there is a risk of the moisture-proof barrier being peeled off due to the long outer peripheral region. Therefore, the hermetic sealing of the scintillator layer may become incomplete, moisture may penetrate into the scintillator layer and cause a problem that deteriorates the characteristics of the scintillator layer.

In addition, the above technique discloses a method for producing a moisture sealing layer for a moisture protection barrier, in which a silicone potting material or the like in a liquid state is applied to the scintillate layer, or within a light-receiving surface side of the radiation detection device, and then the window device is placed on the scintillator layer before the moisture-sealing layer is dried, thereby fixing the moisture-sealing layer. In this method, it is difficult to uniformly form the moisture-sealing layer on a scintillator layer having an irregular surface shape, possibly deteriorating the adhesion. This phenomenon is particularly likely to occur in radiation detection devices having a large area.

In view of the foregoing problems, it is desirable to provide a radiation detection device having a uniform protective film for protecting the scintillator against moisture, which can be easily manufactured, and a method for manufacturing the same.

Summary of the invention

In accordance with one aspect of the present invention, there is provided a radiation detection device comprising: an array of light-receiving devices in which a plurality of light-receiving devices are arranged one- or two-dimensionally on a substrate to form a light-receiving region, and a plurality of connection surfaces electrically connected to the light-receiving devices are arranged in corresponding rows or columns of the light-receiving region outside the light-receiving region, and a scintillator layer deposited on the light-receiving devices for converting radiation into visible light, a radiation-transmittable, a moisture-proof protective film covering at least the scintillator layer and exposing at least the electrical connection surface area of the light-receiving device arrays; and a coating resin coating the peripheral area of the moisture-proof protective film to bond the edge of the moisture-proof protective film to the light-receiving device array.

Consequently, the incident radiation is converted into visible light by the scintillator layer. Since the resulting image of the visible light is detected by the one- or two-dimensionally arranged light-receiving devices, an electrical signal corresponding to the image of the incident radiation is obtained. The scintillator layer has the property of deteriorating by absorbing moisture. However, since the scintillator layer is covered with a moisture-proof protective film and the edge of the moisture-proof protective film is coated with the coating resin, the scintillator layer is completely hermetically sealed to be isolated from the external environment and thus protected against vapor in the air. Furthermore, the area of the electrical connection pad for connection to an external circuit is exposed.

According to another aspect of the present invention, there is provided a method of manufacturing a radiation detection device, the method comprising the steps of: a step of forming a light receiving region by one- or two-dimensionally arranging a plurality of light receiving devices on a substrate and depositing a scintillator layer for converting radiation into visible light on the light receiving devices of a light receiving device array in which a plurality of terminal pads electrically connected to the light receiving devices in corresponding rows or columns of the light receiving region are arranged outside the light receiving region, a step of forming a radiation-transmissible moisture-proof protective film to cover the light receiving device array as a whole, a step of cutting and removing at least part of the moisture-proof protective film outside the scintillator layer covering the terminal pads to expose at least part of the light receiving device array in an area including the terminal pads, and a step of coating the peripheral portion of the moisture-proof protective film with a resin to connect the edge of the moisture-proof protective film to the light receiving devices.

Since the first organic film is formed to cover the entire light-receiving device array, the adhesion between the scintillation layer and the organic film is improved, forming a uniform film. Since the uniform moisture-proof protective film is removed from the pad area after its formation, the pad area is exposed with certainty. Furthermore, since the moisture-proof protective film is coated with a resin along the edge portion serving as a boundary with respect to the exposed area, the edge of the moisture-proof protective film comes into close contact with the underlying surface of the light-receiving device array, thereby improving the Scintillator layer is sealed under the moisture-resistant protective film.

Short description of the drawings

Fig. 1 is a plan view showing an embodiment of the present invention, while Fig. 2 is an enlarged sectional view thereof taken along the line A-A ;

Fig. 3 to 10 are views showing manufacturing steps of the embodiment according to Figs. 1 and 2, and

Fig. 11 is a plan view showing another embodiment of the present invention, while Fig. 12 is an enlarged sectional view thereof taken along the line B-B.

Detailed description of the drawings

In the following, embodiments of the present invention will be explained with reference to the drawings. In order to facilitate the understanding of the explanations, the same reference numerals are used for the same parts in all drawings as far as possible and repeated explanations are omitted. In addition, for ease of understanding, the dimensions and shapes in each drawing are not always identical to those in practice, but include exaggerated parts to facilitate understanding.

Fig. 1 is a plan view showing an embodiment of the present invention, while Fig. 2 is a enlarged sectional view of the outer peripheral portion thereof taken along the line AA.

First, the configuration of this embodiment will be explained with reference to Figs. 1 and 2. On an insulating substrate 1 made of, for example, glass, light-receiving devices 2 for photoelectric conversion are arranged two-dimensionally to form a light-receiving region. Each light-receiving device 2 consists of a photodiode (PD) made of amorphous silicon or a thin film transistor (TFT). The light-receiving devices 2 in the respective rows and columns are electrically connected to each other for reading out signals via signal lines 3. A plurality of pads 4 for outputting signals to an external circuit (not shown) are arranged along the outer peripheral sides of the substrate 1, for example, on two adjacent sides, and are electrically connected to their corresponding plurality of light-receiving devices 2 via signal lines 3. An insulating passivation film 5 is formed over the light-receiving devices 2 and the signal lines 3. Silicon nitride or silicon oxide is preferably used for the passivation film 5. On the other hand, the connection pads 4 for the connection to the external circuit are exposed. In the following, reference is made to this substrate, as well as to the circuit area on the substrate, as an arrangement of light-receiving devices 6.

A scintillator 7 with a columnar structure is formed on the light-receiving region of the array of light-receiving devices 6 for converting incident radiation into visible light. Although various materials can be used for the scintillator 7, Tl-doped CsI or similar having a preferred emission efficiency is preferred. On the scintillator 7, a first organic film 8, an inorganic film 9 and a second organic film 10 are laminated, each transparent to X-rays but impermeable to vapor, thereby forming a protective film 11.

As the first organic film 8 and the second organic film 10, a poly-p-xylylene resin (manufactured by Three Bond Co., Ltd.; brand name: Parylene), particularly poly-p-chloroxylylene (same manufacturer, brand name: Parylene C), is preferably used. The coating made of Parylene has excellent properties for the organic film 8 and 10, such as transmitting very little vapor or gas, having high water repellency and chemical resistance, having excellent electrical insulation properties even as a thin film, and being transparent to radiation and visible light. The details of the coating with Parylene are described in Three Bond Technical News (issue September 23, 1992), and its characteristic features are briefly explained here.

Parylene coating can be done by the chemical vapor deposition (CVD) process, in which vapor deposition takes place on a substrate in vacuum, as in vacuum vapor deposition of metals. This process involves a step of thermally decomposing p-xylene as a starting material and rapidly cooling the resulting product in an organic solvent such as toluene or benzene to obtain di-p-xylylene, which is known to exist as a dimer; a step of thermally decomposing this dimer to produce a stable radical p-xylylene gas;

and a step of producing a poly-p-xylylene film with a molecular weight of about 500,000 by absorption and polymerization of the resulting gas on a material by polymerization.

The pressure at the time of parylene vapor deposition is 13.3 to 26.7 Pa (0.1 to 0.2 Torr), which is higher than the pressure of vacuum vapor deposition of metals, 0.133 Pa (0.001 Torr). In vapor deposition, a monomolecular film covers the entire material to be coated and then parylene is vapor deposited thereon. Consequently, a thin film with a uniform thickness of less than 0.2 µm and free from pinholes can be formed. Therefore, coating of acute angle areas, corner areas and narrow gaps in the micrometer range, which was impossible in liquid form, can be carried out in this way. In addition, coating can be carried out at a temperature close to room temperature, thus without heat treatment or the like at the time of coating. As a result, mechanical stress or thermal distortion cannot occur during curing and the coating also has excellent stability. In addition, a coating is possible for almost any solid material.

For the inorganic film 9, various materials such as those transparent to visible light, opaque or reflective can be used as long as they are transparent to X-rays. Oxidized films of Si, Ti and Cr and thin metal films of gold, silver, aluminum or the like can be used. In particular, a film that reflects visible light is preferably used because it effectively prevents fluorescence generated in the scintillator 7 from escaping, thereby the sensitivity is increased. Here, an example is explained using Al, which is easy to form. Although Al is likely to corrode in air, the inorganic film 9, since it is held between the first organic film 8 and the second organic film 10, is protected from corrosion.

The outer periphery of the protective film 11 extends to the inside of the pads 4 between the corresponding outer periphery of the light receiving region and the light receiving device array 6, exposing the pads 4 for connection to the external circuit. While this protective film 11 is formed by the above-mentioned parylene coating by the CVD method, since it is formed by the CVD method, it is formed to cover the entire surface of the light receiving device array 6. Therefore, in order to expose the pads 4, it is necessary that the protective film 11 formed by the parylene coating is cut inside the pads 4 and the outer part of the protective film 11 is removed. In this case, the protective film would likely peel off from the outer periphery portion serving as the cutting portion. Therefore, the outer peripheral portion of the protective film 11 and the portion of the passivation film 5 of the light-receiving device array 6 on its outer peripheral side are coated and covered with a coating resin 12.

For the coating resin 12, a resin having preferable adhesion properties to the protective film 11 and the passivation film 5, for example, WORLD ROCK No. 801-SET2 (Type 70,000 cP) manufactured by Kyoritsu Chemical Industries Co., Ltd., which is an acrylic adhesive, is preferably used. This resin adhesive is curable after about 20 seconds of UV irradiation with 100 mW/cm². This coating film cured in this way is soft, but has sufficient strength, is excellent in its resistance to moisture, water, contact corrosion and migration, adheres preferentially to various materials such as glass, plastics, etc., and therefore has preferred properties than the coating resin 12.

The manufacturing process for this embodiment is explained below according to Figs. 3 to 10. As shown in Fig. 4, on the light-receiving surface of the light-receiving device array 6 shown in Fig. 3, columnar crystals of Tl-doped CsI are grown by the vapor deposition method to a thickness of 600 µm to form a layer of the scintillator 7.

The CsI constituting the scintillator layer 7 is highly hygroscopic, so that it is dissolved in the air after further exposure to absorbing vapor. To prevent the occurrence of this phenomenon, as shown in Fig. 5, the CVD method is used to cover the entire substrate with parylene in a layer thickness of 10 µm, thereby forming the first organic film 8. Although there are gaps between the columnar crystals of the CsI, parylene can penetrate into these narrow gaps to some extent, whereby the first organic film 8 comes into close contact with the scintillator layer 7. Furthermore, the parylene coating provides a precise, thin film coating with a uniform thickness over the irregular scintillator layer 7. Since parylene can be produced by CVD at a lower vacuum and at normal temperature compared to metal vapor deposition, it can be easily processed.

Thereafter, as shown in Fig. 6, on the surface of the first organic film 8 on the entrance side, an Al film having a thickness of 0.15 µm is laminated by the vapor deposition method, thus forming the inorganic film 9. Then, again by using the CVD method, the surface of the entire substrate is coated with a parylene layer having a thickness of 10 µm, which forms the second organic film 10 (see Fig. 7). This second organic film 10 protects the inorganic film 9 from deterioration due to corrosion.

The protective film 11 thus formed is cut with an excimer laser or the like along the outer periphery of the light receiving region at the part inside the pads 4 between the light receiving region and the outer peripheral region of the light receiving device array 6 as shown in Fig. 8, and then, from the thus cut region, the unnecessary portions of the protective film 11 on the outside thereof and on the back of the entrance surface as shown in Fig. 9 are removed to expose the pads 4 for connection to the external circuit. Since the passivation film 5 and the first organic layer 7 deposited as the lowermost layer of the protective film 11 do not adhere well to each other, the protective layer 11 will easily peel off if the cut outer peripheral region is left as it is. Therefore, as shown in Fig. 10, the outer peripheral portion of the protective film 11 and the part of the passivation film 5 are coated all around and covered with the coating resin 12, which is then cured by UV irradiation, whereby the protective film 11 adheres closely to the light receiving device array 6. As a result, the scintillator 7 is hermetically sealed, whereby Deterioration of resolution due to moisture absorption can be prevented.

The operation of this embodiment will now be explained with reference to Figs. 1 and 2. An X-ray (radiation) incident through the entrance surface passes through the protective film 11 consisting of the first organic film 8, the inorganic film 9, the second organic film 10 to reach the scintillator 7. This X-ray is received by the scintillator 7, which emits visible light in proportion to the dose of the X-ray. Of this emitted visible light, the part in the direction directly opposite to the direction of incidence of the X-ray is reflected by the inorganic film 9. Consequently, almost all of the visible light generated by the scintillator 7 is irradiated on the light receiving device 2 located below the scintillator 7. This achieves efficient detection.

By photoelectric conversion, an electrical signal corresponding to the amount of visible light is generated in each light-receiving device 2 and stored for a predetermined time. Since the amount of visible light reaching the light-receiving device 2 corresponds to the dose of incident X-rays, the electrical signal stored in each light-receiving device 2 corresponds to the dose of incident X-rays, so that an image signal corresponding to an X-ray image is obtained. The image signals stored in the light-receiving devices 2 are read out serially via the signal lines 3 from the connection surfaces 4, conducted to the outside, processed in a predetermined processing circuit, whereby the X-ray image can be displayed.

Although the above explanation regarding the protective film 11 assumes a structure in which an inorganic film 9 is held between first and second organic films 8 and 10 made of parylene, the first organic film 8 and the second organic film 10 may be made of different materials from each other. In addition, if a material having high corrosion resistance is used for the inorganic film 9, the second organic film 10 per se may be omitted.

Although an example is explained here in which the coating resin 12 is formed on the passivation film 5 outside the part of the light-receiving device array 6 formed with the light-receiving devices 2, it will be difficult to form the resin coating 12 in a boundary region between the light-receiving devices 2 and the pad 4 when they are very close to each other. In order to surely expose the pad 4 and securely coat the periphery of the protective film 11 with the coating resin 12, it is preferable that the position of the coating resin 12 is shifted toward the light-receiving devices 2. For this purpose, the scintillator 7 is not formed on the entire surface of the light receiving devices 2, but on the light receiving devices 2 within the effective screen area, omitting the pixels near the terminal surfaces 4. Then, after the protective film 11 is formed over the entire formed layer of the scintillator 7, the protective film 11 is coated with the coating resin 12 on the pixels of the light receiving devices 2 whose upper front surface is not formed with the scintillator 7. In this case, since the pixels near the terminal surface 4 are coated with the coating resin or are free from the scintillator 7 on the front, their sensitivity to radiation is reduced. Consequently, these pixels are useless, thereby reducing the number of effective pixels and the area of the effective screen surface of the light-receiving devices 2. When the light-receiving devices 2 form a large screen surface and have a large number of pixels in total, the proportion of useless pixels is nevertheless small and, depending on the configuration of the devices, they have the advantage of simplifying manufacture.

Referring to Figs. 11 and 12, another embodiment of the present invention will now be explained. Fig. 11 is a plan view of the radiation detection device according to this embodiment, while Fig. 12 is an enlarged sectional view thereof taken along line B-B. Since the basic structure of this embodiment is the same as that shown in Figs. 1 and 2, only their differences will be explained below.

In the embodiment shown in Figs. 11 and 12, the protective film 11 is formed on the entire surface of the light receiving device array 6 on the light receiving surface side and the back side, exposing only the pad array 4. The coating resin 12 is coated along the peripheries (edges) of the protective film 11 to envelop the area of the exposed pad 4. Since the area of the pad 4 is securely exposed and the protective film 11 is securely adhered to the light receiving device array 6 by means of the coating resin 12, the scintillator layer 7 is hermetically sealed, thus achieving a Deterioration caused by moisture absorption is avoided in this embodiment.

This embodiment is effective because it shortens the length of the edge portion serving as a boundary portion, which may cause peeling of the protective film, particularly in the case of CCD or MOS type imaging systems having small terminal areas 4.

Furthermore, although the foregoing explanation refers to radiation detection devices of the so-called surface entry type in which the radiation from the scintillator side is incident on the light-receiving areas, the present invention can also be embodied so that it can be used as a radiation detection device of the so-called rear entry type. Such rear entry type radiation detection devices can be used as a high-energy radiation detection device.

As explained above, in order to protect a highly hygroscopic scintillator, a protective film made of parylene or the like is formed on the scintillator, and edges of the protective film are bonded to the light-receiving device array with a resin coating made of acrylic or the like, thereby hermetically sealing the scintillator layer.

In particular, since the detachment of the protective film from the edges is prevented, the moisture resistance is improved.

In the manufacturing process, the protective film is formed and then unnecessary parts are removed therefrom, whereby the protective film is more easily formed in a uniform state, compared with the case where the protective film is formed only on necessary parts while securely exposing the connection surfaces. In addition, since the protective film penetrates into the gaps between the deposited columnar crystals in the scintillator layer, the adhesion between the protective film and the scintillator layer is increased.

Industrial applicability

The device for detecting radiation according to the embodiments described above is applicable to a wide range of systems for detecting radiation, which are used in particular for medical and industrial X-ray examinations. It can be used in particular instead of the X-ray films which are still frequently used for X-ray examinations of the chest or similar.

It should be noted that the present invention is not limited to the above-described embodiments. It is intended that various modifications and variations of the above-described embodiments may be made without departing from the scope of the present invention as defined in the claims.

Claims (8)

1. A device for detecting radiation, comprising: an arrangement of light-receiving devices (6), in which a plurality of light-receiving devices (2) are arranged one- or two-dimensionally on a substrate (1) to form a light-receiving area, and a plurality of connection surfaces (4) electrically connected to the light-receiving devices (2) are arranged in corresponding rows or columns of the light-receiving area outside the light-receiving area, a scintillator layer (7) deposited on the light-receiving devices (2) for converting radiation into visible light, a radiation-permeable, moisture-resistant protective film (11) which covers at least the scintillator layer (7) and leaves open at least the area of the connection surfaces of the arrangement of light-receiving devices (6), and a coating resin (12) with which the peripheral portion of the moisture-proof protective film (11) is coated to connect the edge of the moisture-proof protective film (11) to the array of light-receiving devices (6). 2. A radiation detection device according to claim 1, wherein the terminal pads (4) are arranged on an outer peripheral region of the substrate (1), the moisture-proof protective film (11) is formed such that it extends to an area between an outer periphery of the light-receiving region and an outer periphery of the array of light-receiving devices (6), and an outer periphery of the moisture-proof protective film (11) is coated with the coating resin (12). 3. A radiation detection device according to claims 1 or 2, wherein the moisture-resistant protective film (11) is composed of a multilayer film made of at least two layers, including an organic film (8, 10) laminated thereon. 4. A radiation detection device according to claim 3, wherein the multilayer film (11) includes at least one inorganic layer (9). 5. A method of manufacturing a device for detecting radiation, comprising: a step of forming a light-receiving region by the one- or two-dimensional arrangement of a plurality of light-receiving devices (2) on a substrate (1) and the deposition of a scintillator layer (7) for converting radiation into visible light on the light-receiving devices (2) of an arrangement of light-receiving devices (6) in which a plurality of connection surfaces (4) connected to the light-receiving devices (2) in corresponding rows or columns of the light-receiving region are electrically connected, are located outside the light-receiving area, a step of forming a radiation-permeable, moisture-resistant protective film (11) for enveloping the entire arrangement of light-receiving devices (6), a step of cutting and removing at least a part of the moisture-resistant protective film (11) outside the scintillator layer (7) covering the connection surfaces (4) in order to expose at least the part of the arrangement of light-receiving devices (6) in an area enclosing the connection surfaces (4), and a step of coating the peripheral portion of the moisture-proof protective film (11) with a resin (12) to bond the edge of the moisture-proof protective film (11) to the array of light-receiving devices (6). 6. A method of manufacturing a radiation detection device according to claim 5, wherein the cutting and removing step includes cutting the moisture-proof protective film (11) along an outer circumference of the scintillator layer (7) at a position between the outer circumference of the scintillator layer (7) and the area of the terminal pads and removing the part of the moisture-proof protective film (11) formed outside the thus-cut surface and on the side opposite to an input surface to expose the terminal pads (4), and wherein the coating step includes coating the thus-cut outer circumference portion of the moisture-proof protective film (11) with a resin (12) to form the outer circumference portion of the moisture-resistant protective film (11) into close contact with the arrangement of light-receiving devices (6). 7. A method of manufacturing a radiation detection device according to claim 5 or 6, wherein the step of forming a moisture-resistant protective film (11) comprises: a sub-step of forming a radiation-permeable first organic film (8) for enclosing the entire arrangement of light-receiving devices (6), and a sub-step of coating at least one film layer (9, 10) on the first organic film (8) in order to form a radiation-permeable, moisture-resistant protective film (11) consisting of a multilayer film made of at least two layers. 8. A method of manufacturing a radiation detection device according to claim 7, wherein the multilayer film (11) includes an inorganic film (9).